Visiting Mars, Again and Again

Visting Mars, Again and Again

Mars is preparing for an invasion from Earth. The rovers Spirit and Opportunity are still traveling across the surface of the Red Planet, but NASA and the European Space Agency are planning to send more missions over the next few years.

Model of the Mars Phoenix lander. The lander’s robotic arm will scrape away surface dirt and ice on Mars, searching for organic molecules. Photo Credit: University of Arizona.

First up is the Mars Phoenix lander. Launched last year, this mission is due to arrive near the Martian north pole on May 25. The lander won’t be able to move around like the rovers — instead, it will stay in one place, scraping away at water ice just beneath the surface in a search for the organic compounds that are thought to be necessary for life.

NASA’s next rover mission is the Mars Science Laboratory, or MSL. A much larger rover than the ones currently on Mars, MSL will collect soil and rock samples and analyze them for organics. The planned launch for MSL is Fall of 2009, with an expected arrival in October 2010.

The European Space Agency also has plans for a rover. Called ExoMars, the projected launch date for this mission is 2013, with arrival in 2014. The ExoMars rover will have a drill that can dig deep into the subsurface, allowing scientists to search for evidence of water and organics.

Astrobiology Magazine’s Helen Matsos recently sat down to talk with Michael Meyer, lead scientist for NASA’s Mars Exploration Program, and Luann Becker, a University of California, Santa Barbara geochemist who has been developing the Mars Organic Molecule Analyzer (MOMA) that will fly on the ExoMars mission.

Astrobiology Magazine (AM): Could you tell me about MOMA and the role will it play in the search for life on Mars?

Luann Becker (LB): MOMA is a mass spectrometer that will look for organic matter in the near-subsurface of Mars. It’s our attempt to improve on the Gas Chromatograph-Mass Spectrometer, or GCMS, from the 1976 Mars Viking mission. We took what we thought was a perfectly good approach to the search for life, added new technology, and hoped this new design would be a better way to evaluate whether life ever occurred on Mars.

MOMA is like a Star Trek tricorder, because we can use it to cover the full gamut of measurements that will answer the question of life. We’ve combined the GCMS that is currently flying on several missions — including Rosetta that is now headed to a comet — and added on our part of the instrument. Ours is the more technically challenging part, and I think it’s got the extra oomph that we need to evaluate the entire suite of possible organics that could be present on Mars.

We know there has to be refractory organic matter on Mars. Mars has been constantly bombarded by meteoritic debris and interstellar dust particles, so there’s been a lot of opportunity for the planet to become enriched with organic matter. We expect organics to at least be in the regolith, maybe only a few meters down.

If we do identify some organic component, we can compare it to what has been found by other instruments that try to find specific organics. Then we’ll be able to address the difficult question of whether something interesting is there, and that will strengthen the case for sample return, to pick up some rocks and bring them back to Earth.

Michael Meyer (MM): It’s interesting that nobody has measured organics on the surface of Mars. It was a big surprise when Viking’s GCMS did not find organics. We think we’re now smart enough to look for organics, and we’re starting our search with Phoenix. Phoenix has an instrument called TEGA, the Thermal Evolved Gas Analyzer. It will heat up a sample and volatilize any organics that are there — they’ll come off as carbon dioxide vapor, and the instrument will measure that. Although it might be difficult to characterize what organics might be there, we’ll at least know whether or not there are organics. That’s a big first step.

Artist’s conception of the Mars Science Laboratory rover, using the ChemCam instrument to analyze a rock. Image Credit: French Space Agency (CNES) and Los Alamos National Laboratory

The mission after Phoenix, the Mars Science Laboratory, or MSL, is going to send a GCMS that will look for a broad range of organic material. But it’s not going to be able to look for the entire suite of organic matter that might be on Mars. To compensate for that, MSL will do a derivatization – take a known molecule and extract organic matter out of the soil with it, and then run it through the instrument.

AM: How might these missions help clarify lingering doubts about the Viking results?

MM: Part of the controversy was with Viking’s Labeled Release Experiment. The concept was that if we added organics and water to the Martian soil, all the Martian organisms in that soil would go to town eating the organic matter. The organics would in the process be broken down into carbon dioxide gas, and we could measure that.

The experiment worked, except according to the GCMS there was no organic matter to start with. Because there’s no organic matter to start with, the presumption is that there could not be any organisms there.

Now, the prevailing theory is that the breakdown of the added organic matter was due to the highly oxidizing nature of the surface of Mars. Mars doesn’t have much of a protective atmosphere or a magnetic field, so the surface is irradiated by ultraviolet light. It’s as if somebody poured peroxide over the surface of Mars and let it sit there — anything organic that fell on that surface would be converted to CO2. Still, even though that’s the prevailing theory, we don’t know if that’s actually true.

LB: Viking was an excellent experiment if you think about the strategy behind it: going to Mars and heating a sample, something we do everyday in our laboratory. We thought the surface would be full of carbon and organic matter. The big surprise was how oxidizing and harsh the surface environment really was. Had we considered that, we may have tried a different approach. For example, we might have tried to go deeper into the subsurface. We were in a wonderful spot with Viking to detect any possible organics, because water ice was probably near the surface. If we had been able to do more, maybe we could have answered that question about organics. Certainly we would have had more compelling results, and then we could have been able to continue at that time with our Mars program. But instead we got ambiguous results – something might be there, but it might not be there. Anytime you get an ambiguous result, that’s considered a non-result.

I still marvel at how successful Viking truly was. After all, had Viking not been measuring other components like the atmosphere, we would never have known that we had Martian meteorites. Trapped gas within those meteorites matched the Martian atmospheric composition determined by Viking. So in a way, Viking is still playing an important role in why we are going back to Mars.

AM: With all the missions that are going to Mars, will we be able to collect enough data to finally give a conclusive answer as to whether Mars has life?

MM: The short answer is, yes. The missions are going to be seeking answers to a couple of different questions. Question one is, “What organics are there?” Question two is, “Where are the organics?” That’s the tough one. We’re talking about a planet where much of its surface is over four billion years old, and organics from its early days have been sitting around for an extended period of time. If any organics from this time period remain, they would have to be in a protected environment such as ice or beneath the surface.

This image, captured by the MRO spacecraft’s HiRISE camera on Feb 9, 2008, shows a portion of the landing ellipse for the Phoenix lander. The surface frost is slowly sublimating away (changing directly from ice to gas) revealing small hexagonal and polygonal patterns in the darker soil beneath the surface. Such polygonal patterns are often found in high latitude and high alpine environments on Earth, and are the result of annual thermal contraction in ice-cemented soil or permafrost that forms a honeycomb network of small fractures below the surface. Click image for larger view. Image Credit: NASA/JPL/University of Arizona.

So there are different places we can look where organics may have been preserved from early in Mars’ history. A side story is that, just like Earth, Mars is getting organics from space all the time. And so the question is, “Where is all that organic material going?” We need to find places where a micrometeorite can land and then get buried or protected from the extreme environment.

LB: Location, location, location… that really is key. We’ll have to use every bit of information we get from the satellites currently flying. The Mars Reconnaissance Orbiter has sophisticated high resolution cameras that are providing detailed images of the Martian surface, and we can use those to find the best targets. Where can we go that will give us the most robust results? I think picking the best locations will be almost as important as any instrument we can come up with. The Phoenix mission is going to be interesting, because it’s landing in one of my favorite locations for looking for organics.

AM: If Phoenix were to get some sort of positive indication, is that enough to say that we’ve detected life on Mars? Or will that just be the first step?

MM: Everybody would be happy if we find organics, because then at least we’ve proved they’re there, as we think they ought to be. Then the big debate would be, “What are they really?” In terms of instrumentation, there’s a degree of how well they can characterize the organics that we find. If we find very degraded organics – like kerogen or coal –it would difficult to say whether that organic matter came from space or if it was from a biological process on Mars.

We are sending missions to three different places. Phoenix is going to dig into the ice near the north pole. Mars Science Laboratory has a little drill, so it’s going to go to wherever there’s exposed bedrock and rocks lying around. ExoMars has a big drill, so it’s going to go deeper down into the surface.

Holden crater is believed to be the site of an ancient, long-lived lake on Mars. Holden crater may contain minerals that formed in the presence of water, making it an excellent place to send a mission to investigate whether Mars ever supported life. Click image for larger view. Image Credit: NASA/JPL/University of Arizona.

Even if they landed on the same spot, they would be sampling different things. So it’s the range of places that we’re going to look, and then the range in the sophistication of the instrumentation that will make a difference in terms of how well we can characterize the results. Life tends to use the same molecules over and over again. For instance, if we find chiral compounds — all left handed or all right handed molecules — the only process we know that has those is life. And we could say, “Slam-dunk, we win, we found life on Mars!” Or we could find something old that contained only certain classes of compounds. That would make us suspicious because we’re lacking the whole kitchen sink, and there would be a great debate.

LB: I think too that an exciting potential outcome of this particular suite of missions is to learn something about our own origin of life. For years we’ve been debating about how life evolved on our own planet some 4 billion years ago. The regolith of Mars is very old, and Mars was probably doing the same thing as Earth back then. It had all the same ingredients — it had water, it had an atmosphere, and it potentially had sedimentary rocks. Wouldn’t it be remarkable if we get that piece of the puzzle that has been completely erased from the Earth? To discover whatever it was that led to the DNA and RNA world, which is so unique and absolutely prolific with respect to life. Wouldn’t it be remarkable if we found that precursor molecule that we think was so important to getting life started? Now that would be an important and very exciting result!